The invention relates to the method and apparatus for planarizing a layer of photoresist during semiconductor device manufacturing processes.
Very large scale integrated circuit devices typically are manufactured on a substrate, such as a silicon wafer, by a sequence of material additions, such as low pressure chemical vapor depositions, sputtering operations, among others; material removals, such as wet etches, reactive ion etches, among others; and material modifications, such as oxidations, ion implants, among others. Typically, these physical and chemical operations interact with the entire substrate. For example, if a substrate is placed into an acid bath, the entire surface of the substrate will be etched away. In order to build very small electrically active devices on a substrate, the impact of these operations has to be confined to small, well-defined, regions.
Lithography in the context of VLSI manufacturing includes the process of patterning openings in photosensitive polymers, sometimes referred to as xe2x80x9cphotoresistsxe2x80x9d or xe2x80x9cresistsxe2x80x9d, which define small areas in which substrate material is modified by a specific operation in a sequence of processing steps.
The radiation preferably causes desired photochemical reactions to occur within the photoresist. Preferably, the photochemical reactions alter the solubility characteristics of the photoresist, thereby allowing removal of certain portions of the photoresist. Photoresists can be negative photoresist or positive photoresist materials.
A negative photoresist material is one which is capable of polymerizing and being rendered insoluble upon exposure to radiation. Accordingly, when employing a negative photoresist material, the photoresist is selectively exposed to radiation, causing polymerization to occur above those regions of the substrate which are intended to be protected during a subsequent operation. The unexposed portions of the photoresist are removed by a solvent which is inert to the polymerized portion of the photoresist. Such a solvent may be an aqueous solvent solution.
Positive photoresist material is a material that, upon exposure to radiation, is capable of being rendered soluble in a solvent in which the unexposed resist is not soluble. Accordingly, when applying a positive photoresist material the photoresist is selectively exposed to radiation, causing the reaction to occur above those portions of the substrate which are not intended to be protected during the subsequent processing period. The exposed portions of the photoresist are removed by a solvent which is not capable of dissolving the exposed portion of the resist. Such a solvent may be an aqueous solvent solution.
Selectively removing certain parts of the photoresist allows for the protection of certain areas of the substrate while exposing other areas. The remaining portions of the photoresist may be used as a mask or stencil for processing the underlying substrate. For example, the openings in the mask may allow diffusion of desired impurities through the openings into the semiconductor substrate. Other processes are known for forming devices on a substrate.
The manufacturing of VLSI chips typically involves the repeated patterning of photoresists, followed by etch, implant, deposition, or other operation, and ending with the removal of the exposed photoresist to make way for the new photoresist to be applied for another iteration of this process sequence.
Often, to help ensure uniform processing of materials, the upper surface of a layer of a material deposited on a substrate may be processed to lie in substantially only one plane. Such processes are typically referred to as planarization. One example of materials that may be planarized includes polycrystalline silicon. However, techniques utilized to xe2x80x9cplanarizexe2x80x9d materials have not been applicable to photoresist.
Aspects of the present invention provide a method for planarizing a layer of photoresist on a substrate. The method includes, a step of exposing the layer of photoresist to wavelengths of radiation that the photoresist is sensitive to. The radiation is directed at the layer of photoresist at an oblique angle with respect to a major dimension of the layer of photoresist. According to the method, the photoresist is then developed.
Additional aspects of the present invention provide a device for planarizing a layer of photoresist on a substrate. The device includes a radiation source for exposing the photoresist to radiation directed at the photoresist at an oblique angle with respect to a major dimension of the layer of photoresist.
Further aspects of the present invention provide a method for forming a semiconductor device. The method includes forming at least one trench in a substrate. The layer of photoresist is deposited on the substrate and in the at least one trench. Deposition of photoresist in the at least one trench results formation of recesses in an upper surface of the layer of photoresist. The layer of photoresist is exposed to wavelengths of radiation that the photoresist is sensitive to. The radiation is directed at the layer of photoresist at an oblique with respect to a major dimension of the layer of photoresist. Additionally, the radiation is directed at the layer of photoresist from a plurality of angles around the substrate. The layer of photoresist is developed, wherein after developing, the recesses are at least substantially eliminated. The photoresist is then subjected to further processing.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.